How Microsoft Improved the Chromium Web Browser

Since transitioning its Edge browser to the open-source Chromium project, Microsoft has become one of the most active contributors to the platform. By committing thousands of code changes directly to the upstream repository, Microsoft has significantly enhanced the core browser engine that powers not only Edge, but also Google Chrome, Brave, Vivaldi, and Opera. This article provides a direct look at Microsoft's key engineering contributions to Chromium, focusing on advancements in scrolling responsiveness, Windows accessibility, system performance, and hardware integration.

Scrolling Responsiveness and Input Latency

Before adopting Chromium, Microsoft’s legacy Edge browser was widely praised for its smooth and responsive scrolling. Upon joining the Chromium project, Microsoft engineers worked to bring that same fluidity to the open-source engine.

  • Percent-Based Scrolling: Microsoft overhauled how Chromium handles mouse wheel and scrollbar inputs. Instead of scrolling a fixed number of pixels, engineers implemented percent-based scrolling, which scrolls a percentage of the viewport. This made scrolling feel much more natural across screens of varying resolutions and sizes.
  • Main Thread Independence: Microsoft helped move scrolling operations away from the browser's busy main thread to the compositor thread. This ensures that even if a webpage is running heavy JavaScript, the user can still scroll smoothly without stuttering or freezing.
  • Touch and Touchpad Refinements: Engineers improved inertia curves and gesture recognition for Windows Precision Touchpads and touchscreens, eliminating the robotic feel that previously plagued Chromium browsers on Windows laptops.

Windows Accessibility Overhaul

Microsoft made massive strides in modernizing how Chromium interacts with assistive technologies on the Windows operating system.

  • UI Automation (UIA) Support: Historically, Chromium relied on older accessibility APIs. Microsoft engineered native support for the modern Windows UI Automation framework. This allowed screen readers like Windows Narrator, JAWS, and NVDA to communicate much more efficiently with the browser, reducing crashes and improving navigation speed for visually impaired users.
  • High Contrast Mode: Microsoft introduced standardized support for Windows High Contrast themes. By implementing the CSS forced-colors media query upstream, Chromium browsers can now automatically adapt web content to respect the high-contrast color schemes set by the user in Windows.
  • Caret Browsing and Focus Indicators: Microsoft improved keyboard navigation by making focus rings more visible and refining Caret Browsing, which allows users to navigate webpage text using a movable cursor via the keyboard, just like in a word processor.

Memory Usage and Battery Efficiency

Chromium has a historical reputation for high RAM consumption and battery drain. Microsoft utilized its deep knowledge of the Windows operating system to optimize how the browser manages system resources.

  • Background Tab Throttling: Microsoft contributed code to more aggressively restrict the CPU usage of background tabs. This laid the groundwork for features like "Sleeping Tabs," which free up memory and prevent inactive websites from draining laptop batteries.
  • Media Caching: Engineers altered how Chromium buffers and caches streaming video. By reducing the frequency with which the browser wakes up the network hardware and disk drive during video playback, Microsoft significantly extended battery life for users streaming high-definition content.
  • Memory Allocation Improvements: Microsoft collaborated with Google to optimize memory management using Windows-specific APIs, ultimately helping the browser reclaim unused memory faster and reducing the overall RAM footprint of open tabs.

Hardware Integration and Ink Support

To make web applications feel as responsive as native desktop apps, Microsoft bridged the gap between web standards and hardware capabilities.

  • Delegated Ink Trails: Using a stylus on the web previously suffered from noticeable lag between the pen tip and the drawn line. Microsoft introduced the Delegated Ink API to Chromium, allowing the operating system's compositor to draw the ink trail one frame ahead of the browser. This reduced pen latency to near-zero on supported hardware.
  • Native ARM64 Support: Microsoft did the heavy lifting to compile and optimize Chromium natively for Windows on ARM processors. This prevented the browser from having to run in a slow emulation mode on ARM-powered laptops, drastically improving speed and battery life on those devices.
  • Spellcheck Integration: Instead of forcing Chromium to rely solely on its built-in open-source dictionary, Microsoft integrated the native Windows Spellcheck API. This allowed the browser to recognize custom user dictionaries, better handle multiple languages simultaneously, and correctly identify URLs and acronyms.